Animate when double-clicking on a folder to expand it (fixed #404)
Don't show a copy mouse icon when dropping is not allowed at this location
Merge pull request #406 from dinhviethoa/398-dont-show-plus-icon-when-dnd-not-allowed

Fixed mouse icon while dragging over items.
Merge pull request #405 from dinhviethoa/404-double-click-animation

Animate when double-clicking on a folder to expand it
Fixed duplicate items in menu + crash on Polymer UI launch
Merge pull request #408 from ussuri/fix-broken-uis

Fixed duplicate items in menu + crash on Polymer UI launch
Merge branch 'master' of https://github.com/dart-lang/spark into new_dialogs
more cleanup